Patent GB-777439-A (GB)
Title: Remote control and signalling system
Inventor: LEEDS CHARLES MURRAY
IPC: H04Q9/14
Filed: 1953-01-27
Abstract: 777,439. Electric selective signalling. SERVO ELECTRONIC SWITCH & SIGNAL CO., [formerly ELECTRONIC SWITCH & SIGNAL CO.]. Jan. 27, 1953, No. 2376/53. Class 40 (1). In a remote control system, the transmitter transmits pulses of A.C. which step switches at a plurality of receivers, and information concerning the location of the equipment to be controlled and the nature of the control is transmitted by varying the duration of a plurality of space periods between the pulses at different positions in the stepping cycle of the switch. Answer-back mechanism is also provided. Transmitter, Fig. 2. A control operation is effected at the central station by closing one of the switches 38 indicative of the field station concerned, the operation of a key 46 indicative of the control operation to be performed, and the pressing of a start button 48. The last brings up relay SSR which causes relay PGR to interact with the magnet TSS to step the reverse-drive switch SS. In each position of the switch the magnet contacts d energize the transmitter 18 to transmit an A.C. signal (200 kc.) to line. When, however, the wiper S-3 reaches a position marked by an operated contact 38 or 46, relay CR operates to delay PGR from operating until CPR has operated, thereby increasing the interval between the A.C. signals transmitted to line. Relay SSR, which holds during the stepping, also brings up CDR which is slow to release so that a further operation of the push-button 48 cannot be effective until some time after the return home of the switch SS, thereby giving the corresponding switch at the outstation time to home if for any reason it loses synchronism with SS. Receiver, Fig. 3. Impulses of A.C. operate the receive relay RR intermittently and thereby step the switch RSS. Relay LPR operates when the switch moves off-normal. When the first lengthened interval between signals occurs, slow-to-operate relay TR comes up and operates FSR which holds for the duration of the next impulse thereby allowing one of the relays R1 . . . R2 to operate over wiper RS1 and lock. Each field station has a set of relays R1 . . . R2, each relay corresponding to the position of RSS indicative of a field station. The contacts of these relays are so arranged in a circuit for relay STPR that if a relay is operated which does not correspond with its field station (e.g. R2 is operated in field station number 1) then STPR operates and renders the subsequent signals of the cycle ineffective as regards the equipment control relays R3 . . . R11. Otherwise STPR remains down and the next lengthened interval causes the operation of one of these relays which locks and effects the necessary control. When the switch reaches its home position all relays R1 . . . R2, except that corresponding to its own field station (R1), are released by the energization of an opposing winding. In any subsequent cycle in which a lengthened interval does not occur in a position corresponding to the field station (say number 1) of the receiver concerned the corresponding relay is released by the energization of an opposing winding over wiper RS2, so that the subsequent control signal is not effective at that station. To cancel the control a cycle must be sent containing a lengthened signal in a position corresponding to R1, to prevent the operation of STPR at that station, and interval of normal length must subsequently occur at the position corresponding to the operated control relay which is then released by the energization of an opposing winding over RS2. If a space period of very long duration occurs when RSS is off-normal (e.g. due to the central and field switches losing synchronism) slow-to-operate relay EHR comes up to home the switch. Answer-back mechanism. This is similar to the outward control mechanism with the exception that since each field station transmits on a different frequency station identities are not signalled by increasing the space period. The transmit mechanism is triggered off by any change in condition of the equipment which releases a normally operated relay whose contacts replace the push-button 48 of Fig. 2. The transmitter also includes a normally operated relay which falls away in the event of a local power failure to disable the transmitter and cannot reoperate until the switch is in its home position, thereby preventing the transmission of spurious signals when the switch commences re-stepping on restoration of the power supply. Modifications. The signals instead of consisting of pulses of a certain frequency may consist of alternate pulses of two frequencies with a pulse of one of these frequencies lengthened to indicate the identity of the field station or the control to be effective. Alternatively instead of lengthening one of the pulses a pulse of a third frequency could be substituted or superimposed. Frequency modulation of the A.C. may be used to replace the pulse and interval of the system described. Separate channels may be used for the outward control signals and the answer-back signals. The switches of Figs. 2 and 3 may be replaced by relay chains and discrimination over the length of the interval may be effected by a resistance-condenser gas-tube combination. Connection of transmitter and receiver to the transmission line may be effected over conjugate arms of a hybrid coil. The substations may be represented by combinations of lengthened space intervals and a modified form of receiver, Fig. 14 (not shown), is described for recognizing such combinations.